1. Field of the Invention
The present invention relates to ink jet heads, ink jet head production methods, and imaging apparatuses employing such ink jet heads, and more particularly to an ink jet head for image formation employed in imaging apparatuses such as copiers, facsimile machines, and printers, a method of producing such an ink jet head, and an imaging apparatus employing such an ink jet head.
2. Description of the Related Art
A recent trend toward color recording has boosted a demand for imaging apparatuses using a drop-on-demand ink jet head, so that such imaging apparatuses has been commonly used. In addition, there has been a strong demand for an increase in the number of nozzles and nozzle density for achieving higher image quality and a higher recording rate.
In response to such a demand, there has been produced an ink jet head that ejects ink pressurized by the restoring force of an electrostatic diaphragm deformed by electrostatic force generated between the electrostatic diaphragm and a corresponding counter electrode. Such an ink jet head, which employs a diffusion layer formed on a silicon (Si) substrate as counter electrodes, has a simple structure and operation principle. Therefore, energetic efforts have been made to develop an ink jet head of this type as one of favorable means for realizing high nozzle density in ink jet heads.
Japanese Laid-Open Patent Application No. 6-55732 represents this kind of prior art. This document points out the possibility of forming driver devices in single-crystal silicon forming ink chambers and diaphragms in an electrostatic ink jet head as shown in FIG. 1. According to FIG. 1, which is a sectional view of a bit (an ink jet unit) of the ink jet head, the ink jet head includes a Si substrate 71, a cover glass 72, a boro-silicate glass substrate 73, a counter electrode 74, a nozzle 75, a cavity 76, a diaphragm 77, a channel 78, an ink chamber 79, an ink supply pipe 80, a power supply 81, a seal 82, an insulating film 83, a common electrode 84, and a contact 85.
It is common knowledge that a head cannot be driven at a high speed unless a value of resistance of a diaphragm is lowered. That is, the impurity concentration of single-crystal silicon is increased to lower the value of resistance so that the head is driven at a high speed. However, it is impossible to form a device in the single-crystal silicon whose impurity concentration is increased because the impurity concentration is too high. Therefore, although the above-described document points out the possibility of forming the driver devices in the single-crystal silicon, the document, in practice, only employs a conventional method of forming a thin metal film on the diaphragms. Such a structure, however, lowers junction quality of an electrode substrate and an ink chamber substrate, thus causing a problem.
On the other hand, Japanese Laid-Open Patent Application No. 7-125196, which is another prior art example, discloses a technique for charging and discharging by using an active element in driving a diaphragm. However, this document only points out simply that the active element is used in charging and discharging, and has no direct relation to an idea of actively forming the active element in a Si substrate, which is an aim of the present invention.
Japanese Laid-Open Patent Application No. 2000-52544 discloses a technique for forming a diffusion layer into individual electrodes, and in this respect, this application has the same idea as the present invention. However, this application is totally different from the present invention in electrode structure.
Further, in an electrostatic ink jet head ejecting ink by using the restoring force of elastic diaphragms, each diaphragm inevitably has a width in the direction of its shorter side reduced as nozzle density increases. The displacement of each diaphragm is proportional to the fourth power of its shorter-side length, thus requiring a very high driving voltage. For instance, if each diaphragm has a thickness of about 1.5 xcexcm but a shorter-side length of 55 xcexcm, the driving voltage becomes as high as about 100 V. The number of nozzles increases as the nozzle density increases. Therefore, an increase in the driving voltage boosts the cost of the driving circuit of each bit, thus resulting in extremely high total costs.
It is a general object of the present invention to provide an ink jet head in which the above-described disadvantages are eliminated, a method of producing such an ink jet head, and an imaging apparatus using such an ink jet head.
A more specific object of the present invention is to provide an ink jet head in which the number of nozzles and nozzle density are increased to satisfy a demand for high-quality images and high-speed recording in an ink jet imaging apparatus, and more particularly, an ink jet head made operable at a high speed by forming an active element on an electrode substrate.
Yet another more specific object of the present invention is to provide a method of producing such an ink jet head at low costs by fabricating an inexpensive driving circuit by forming a high-voltage driving active element such as a MOS transistor in a substrate.
It is also more specific object of the present invention to provide an imaging apparatus using such an ink jet head.
The above objects of the present invention are achieved by an ink jet head including: a liquid chamber for containing ink, the liquid chamber being formed in a first substrate; a diaphragm formed in the first substrate to serve as a bottom of the liquid chamber; an individual electrode formed on a second substrate, the individual electrode being formed of a refractory metal and a compound thereof; and an active element forming a driving circuit for driving the diaphragm, the active element being formed in the second substrate, wherein the diaphragm is deformable by electrostatic force generated between the diaphragm and the individual electrode and exerts restoring force of the diaphragm to pressurize the liquid chamber so that the ink is ejected from the ink jet head.
According to the above-described ink jet head, since the driving active element for high voltage is formed on the substrate, the output of the driving integrated circuit may be a low voltage, thus reducing the costs of the driving circuit.
The above objects of the present invention are also achieved by an ink jet head including: a liquid chamber for containing ink, the liquid chamber being formed in a first substrate; a diaphragm formed in the first substrate to serve as a bottom of the liquid chamber; an individual electrode formed on a second substrate; and a MOS transistor formed in the second substrate as an active element forming a driving circuit for driving the diaphragm, wherein the diaphragm is deformable by electrostatic force generated between the diaphragm and the individual electrode and exerts restoring force of the diaphragm to pressurize the liquid chamber so that the ink is ejected from the ink jet head.
According to the above-described ink jet head, the MOS transistor and the individual electrode are formed on the same substrate. Therefore, although at least one high-voltage driving power source is required, a signal voltage applied to the gate of each bit of the ink jet head may be low, thus reducing the costs of the driving integrated circuit of the ink jet head.
The above objects of the present invention are also achieved by an ink jet head including: a liquid chamber for containing ink, the liquid chamber being formed in a first substrate; a diaphragm formed in the first substrate to serve as a bottom of the liquid chamber; a film of a thin film semiconductor material formed on a second substrate; an individual electrode formed on the second substrate and including the thin film semiconductor material; and an active element forming a driving circuit for driving the diaphragm, the active element being formed on the second substrate and including the thin film semiconductor material, wherein the diaphragm is deformable by electrostatic force generated between the diaphragm and the individual electrode and exerts restoring force of the diaphragm to pressurize the liquid chamber so that the ink is ejected from the ink jet head.
The above objects of the present invention are also achieved by an imaging apparatus including an ink jet head including: a liquid chamber for containing ink, the liquid chamber being formed in a first substrate; a diaphragm formed in the first substrate to serve as a bottom of the liquid chamber; an individual electrode formed on a second substrate, the individual electrode being formed of a refractory metal and a compound thereof; and an active element forming a driving circuit for driving the diaphragm, the active element being formed in the second substrate, wherein the diaphragm is deformable by electrostatic force generated between the diaphragm and the individual electrode and exerts restoring force of the diaphragm to pressurize the liquid chamber so that the ink is ejected from the ink jet head.
The above objects of the present invention are also achieved by an imaging apparatus including an ink jet head including: a liquid chamber for containing ink, the liquid chamber being formed in a first substrate; a diaphragm formed in the first substrate to serve as a bottom of the liquid chamber; an individual electrode formed on a second substrate; and a MOS transistor formed in the second substrate as an active element forming a driving circuit for driving the diaphragm, wherein the diaphragm is deformable by electrostatic force generated between the diaphragm and the individual electrode and exerts restoring force of the diaphragm to pressurize the liquid chamber so that the ink is ejected from the ink jet head.
The above objects of the present invention are also achieved by an imaging apparatus including an ink jet head including: a liquid chamber for containing ink, the liquid chamber being formed in a first substrate; a diaphragm formed in the first substrate to serve as a bottom of the liquid chamber; a film of a thin film semiconductor material formed on a second substrate; an individual electrode formed on the second substrate and including the thin film semiconductor material; and an active element forming a driving circuit for driving the diaphragm, the active element being formed on the second substrate and including the thin film semiconductor material, wherein the diaphragm is deformable by electrostatic force generated between the diaphragm and the individual electrode and exerts restoring force of the diaphragm to pressurize the liquid chamber so that the ink is ejected from the ink jet head.
According to any of the above-described apparatuses, the production costs of the driving circuit for driving each bit of the ink jet head of this imaging apparatus are kept low by lowering a driving voltage even when the number of bits is increased for a high-speed recording purpose. Accordingly, any of the above-described apparatuses is also producible at low costs.
The above objects of the present invention are further achieved by an ink jet head production method including the steps of: (a) providing first and second substrates; (b) forming an individual electrode and an active element in the first substrate; (c) forming a liquid chamber and a diaphragm in the second substrate; and (d) bonding the first and second substrates.
According to the above-described method, the liquid chamber and the diaphragm are produced after the first (electrode) substrate is produced by a conventional semiconductor production method. Therefore, a semiconductor production process apt to be affected by alkali ions and a liquid chamber production process using alkali ions are completely separable.